1. Field of the Invention
The present invention relates to an image pickup lens and particularly, to a single image pickup lens which is used in an image pick-up device, e.g., a CCD camera, utilizing an image pickup element such as CCD, CMOS and the like mounted on a potable computer, a visual telephone and the like, and which can be reduced in size and weight.
2. Description of the Related Art
In recent years, multimedia have been developed remarkably, and for example, the demand for a CCD camera mounted on a portable computer, a visual telephone and the like is being increased remarkably. Such a CCD camera is required to be mounted in a limited space and for this reason, it is desired that the CCD camera is small in size and lightweight.
Therefore, it is also desired that an image pickup lens used in such a CCD camera is likewise small in size and lightweight.
A so-called single-lens system employing a single lens is conventionally used as such an image pickup lens system.
There is such a conventionally known image pickup lens in a single-lens system, which is disclosed, for example, in Japanese Patent Application Laid-open No.6-88939 and the like.
The known image pickup lens is formed so that the radius of curvature of a second face of the lens is set in a range of 0.5 to 0.63 times the focal length thereof, and the Abbe constant is set smaller than 50.
In the conventional image pickup lens disclosed in Japanese Patent Application Laid-open No. 6-88939, however, in an image pickup element used presently in relatively many fields, an intended effect can be provided, but recently, a further reduction in size of the image pickup element is desired. For example, if the entire optical system is reduced in size in the use of a lens for an image pickup element having a size as small as 1/6 inches or 1/8 inches, the radius of curvature of a second face of the lens is set in a range of 0.5 to 0.63 times the focal length thereof. This results in a problem that the curvature of a second face of the lens is extremely large and hence, it is extremely difficult to process the lens and further, the lens is dim. Moreover, another problem is that the spherical aberration and the coma are increased, because the curvature of the second face of the lens is increased.